v3.24.3
Label Element Value
Risk Return Abstract rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName First Trust Exchange-Traded Fund III
Prospectus Date rr_ProspectusDate Dec. 02, 2024
First Trust Merger Arbitrage ETF  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Summary Information
Objective [Heading] rr_ObjectiveHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Investment Objective</span>
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The First Trust Merger Arbitrage ETF's (the “Fund”) investment objective is to seek to provide investors with capital appreciation.
Expense [Heading] rr_ExpenseHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Fees and Expenses of the Fund</span>
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy, hold and sell shares of the Fund. Investors may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption <span style="color:#000000;font-family:Arial;font-size:9.00pt;font-weight:bold;">Shareholder Fees</span> <br/><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(fees paid directly from your investment)</span>
Operating Expenses Caption [Text] rr_OperatingExpensesCaption <span style="color:#000000;font-family:Arial;font-size:9.00pt;font-weight:bold;">Annual Fund Operating Expenses</span> <br/><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(expenses that you pay each year as a percentage of the value of your investment)</span>
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Portfolio Turnover</span>
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 301% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 301.00%
Expense Example [Heading] rr_ExpenseExampleHeading <span style="color:#000000;font-family:Arial;font-size:9.00pt;font-style:italic;font-weight:bold;">Example</span>
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds.The example assumes that you invest $10,000 in the Fund for the time periods indicated and then hold or sell all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain at current levels. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Principal Investment Strategies</span>
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock Under normal market conditions, the Fund seeks to achieve its investment objective by establishing long and short positions in the equity securities of companies that are involved in a publicly-announced significant corporate event, such as a merger or acquisition. The Fund’s portfolio may include equity securities issued by U.S. and non-U.S. companies, including American Depositary Receipts (“ADRs”). The Fund may invest in securities issued by small, mid and large capitalization issuers. The Fund’s investment sub-advisor, First Trust Capital Management L.P. (“First Trust Capital Management” or the “Sub-Advisor”), generally seeks to take advantage of the return opportunity presented by the natural deal spread that emerges after the announcement of a merger or acquisition by purchasing the stock of the company being acquired (the “target company”), while shorting the stock of the company acquiring the target company’s stock (the “acquiring company”). The profit which may be realized is the “spread,” or difference in price between the trading price of the target company’s stock following the announcement of the corporate event and the contractual price to be paid for the target company stock in the future when the transaction closes. Such a spread typically exists due to the uncertainty regarding whether the announced merger, acquisition or other corporate event will close, and if it closes, that such transaction will be at the initially proposed economic terms. Only the securities of companies involved in publicly-announced transactions are eligible for inclusion in the Fund’s portfolio. Merger arbitrage, when executed well, has the potential to produce a differentiated and robust absolute return stream. In deciding upon which opportunities to invest in, the Sub-Advisor assesses a number of factors, including, but not limited to, the probability that the merger will be completed, the attractiveness of a transaction relative to others in the arbitrage universe, and any unique risks which may decrease the likelihood that a transaction will close. Every transaction has its unique set of elements, and the Sub-Advisor’s investment process relies on real-time quantitative-based research to evaluate how attractive each transaction is relative to other deals in the arbitrage universe. The Fund adheres to that quantitative criteria to separate which deals to invest in and which to avoid. In the event that the Sub-Advisor cannot find enough securities that satisfy its investment criteria, the Fund may hold a significant amount of cash or cash equivalents. During periods of market stress or when merger and acquisition activity is low, the availability of transactions of the type in which the Fund invests may be significantly limited. To the extent the Fund has a large cash position, the Fund is less able to satisfy its investment objective. As of October 31, 2024, 28.63% of the Fund’s assets consisted of investable cash and/or cash equivalents. Due to the current market environment, it is expected that the Fund may maintain a large cash position for the foreseeable future. The Sub-Advisor intends to engage in short selling. Short selling is a technique that allows an investor (such as the Fund) to profit from the falling price of a security. It involves selling a security that has been borrowed from a third-party with the intention of buying an identical security back at a later date to return to that third-party. The Fund’s short positions may be significant, however, the Fund will at all times comply with the regulatory requirements of the Securities and Exchange Commission with respect to coverage of the Fund’s short positions. The Fund intends to invest the proceeds from a sale of a borrowed security in cash or cash equivalents, including money market funds. The Fund’s investment strategy may include active and frequent trading. The Fund may invest up to 10% of its net assets in stock, warrants, and other securities of special purpose acquisition companies (“SPACs”). A SPAC is a publicly listed acquisition vehicle, whereby one or more sponsors raise a pool of capital with the special purpose of acquiring a private operating company. SPACs often have pre-determined time frames to merge with an operating company (typically two years), and if no merger takes place during that time frame the SPAC will liquidate. A SPAC generally offers units, each comprised of one share of common stock and a warrant (or portion of a warrant) to purchase common stock. A warrant is a security that allows its holder to purchase a specified amount of common stock at a specified price for a specified time. Unless and until an acquisition is completed, a SPAC generally invests its assets (less a portion retained to cover expenses) in U.S. government securities, money market securities and cash. If an acquisition that meets the requirements for the SPAC is not completed within a pre-established period, the invested funds are returned to the entity’s shareholders. The Fund will generally dispose of SPAC interests held by the Fund prior to the completion of an acquisition. Depending on the relative market price of the SPAC securities and the net asset value of the underlying U.S. government securities, money market securities and cash held by the SPAC, the Fund may either sell the securities at their current market price or redeem them with the SPAC in accordance with the redemption terms applicable to such securities. As of October 31, 2024, the Fund had significant investments in health care companies, although this may change from time to time. To the extent the Fund invests a significant portion of its assets in a given jurisdiction or investment sector, the Fund may be exposed to the risks associated with that jurisdiction or investment sector. The Fund is classified as “non-diversified” under the Investment Company Act of 1940, as amended (the “1940 Act”).
Risk [Heading] rr_RiskHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Principal Risks</span>
Risk Caption rr_RiskCaption <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">You could lose money by investing in the Fund.</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">An investment in the Fund is not a deposit of a bank and is not insured or </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;"> There can be no assurance that </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">the Fund’s investment objective will be achieved. The order of the below risk factors does not indicate the significance of any </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">particular risk factor.</span>
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Annual Total Return</span>
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value as well as the average annual Fund returns. The bar chart and table provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual total returns based on net asset value compared to those of a market index and a broad-based market index.The Fund’s performance information is accessible on the Fund’s website at http://www.ftportfolios.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value as well as the average annual Fund returns. The bar chart and table provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual total returns based on </span><span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">net asset value compared to those of a market index and a broad-based market index.</span>
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress <span style="font-family:Arial;font-size:9.00pt;">http://www.ftportfolios.com</span>
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture <span style="color:#000000;font-family:Arial;font-size:9.00pt;">The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.</span>
Bar Chart [Heading] rr_BarChartHeading <span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">First Trust Merger Arbitrage ETF</span> <br/><span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">Calendar Year Total Returns as of 12/31 </span><span style="font-family:Arial;font-size:7pt;font-weight:bold;position:relative;top:-3.25pt;">(1)</span>
Bar Chart Footnotes [Text Block] rr_BarChartFootnotesTextBlock (1)The Fund's calendar year-to-date total return based on net asset value for the period 12/31/23 to 09/30/24 was -0.60%.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock During the periods shown in the chart above:ReturnPeriod EndedBest Quarter2.20%September 30, 2023Worst Quarter-0.62%June 30, 2023Year-to-Date-0.60%September 30, 2024
Performance Table Heading rr_PerformanceTableHeading <span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">Average Annual Total Returns for the Periods Ended December 31, 2023</span>
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged <span style="font-family:Arial;font-size:8.10pt;font-style:italic;">Effective as of August 1, 2024, the S&P Merger Arbitrage Total Return Index replaced the Credit Suisse Merger Arbitrage Liquid Index, which is no longer available for use by the Fund.</span>
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate <span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax.</span>
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;font-style:italic;">IRAs</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">) or employee-sponsored retirement plans.</span>
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher <span style="font-family:Arial;font-size:9.00pt;">Returns after taxes on distributions reflect the taxed return on the payment of dividends </span><span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for </span><span style="font-family:Arial;font-size:9.00pt;">an index do not include expenses, which are deducted from Fund returns, or taxes.</span>
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax.Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for an index do not include expenses, which are deducted from Fund returns, or taxes.Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.
First Trust Merger Arbitrage ETF | Risk Lose Money [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock You could lose money by investing in the Fund.
First Trust Merger Arbitrage ETF | Risk Not Insured Depository Institution [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
First Trust Merger Arbitrage ETF | Authorized Participant Concentration Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock AUTHORIZED PARTICIPANT CONCENTRATION RISK. Only an authorized participant may engage in creation or redemption transactions directly with the Fund. A limited number of institutions act as authorized participants for the Fund. To the extent that these institutions exit the business or are unable to proceed with creation and/or redemption orders and no other authorized participant steps forward to create or redeem, the Fund’s shares may trade at a premium or discount (the difference between the market price of the Fund's shares and the Fund's net asset value) and possibly face delisting and the bid/ask spread (the difference between the price that someone is willing to pay for shares of the Fund at a specific point in time versus the price at which someone is willing to sell) on the Fund’s shares may widen.
First Trust Merger Arbitrage ETF | Counterparty Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock COUNTERPARTY RISK. Fund transactions involving a counterparty are subject to the risk that the counterparty will not fulfill its obligation to the Fund. Counterparty risk may arise because of the counterparty’s financial condition (i.e., financial difficulties, bankruptcy, or insolvency), market activities and developments, or other reasons, whether foreseen or not. A counterparty’s inability to fulfill its obligation may result in significant financial loss to the Fund. The Fund may be unable to recover its investment from the counterparty or may obtain a limited recovery, and/or recovery may be delayed.
First Trust Merger Arbitrage ETF | Current Market Conditions Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock CURRENT MARKET CONDITIONS RISK. Current market conditions risk is the risk that a particular investment, or shares of the Fund in general, may fall in value due to current market conditions. As a means to fight inflation, which remains at elevated levels, the Federal Reserve and certain foreign central banks have raised interest rates; however, the Federal Reserve has recently lowered interest rates and may continue to do so. U.S. regulators have proposed several changes to market and issuer regulations which would directly impact the Fund, and any regulatory changes could adversely impact the Fund’s ability to achieve its investment strategies or make certain investments. Recent and potential future bank failures could result in disruption to the broader banking industry or markets generally and reduce confidence in financial institutions and the economy as a whole, which may also heighten market volatility and reduce liquidity. Additionally, challenges in commercial real estate markets, including rising interest rates, declining valuations and increasing vacancies, could have a broader impact on financial markets. The ongoing adversarial political climate in the United States, as well as political and diplomatic events both domestic and abroad, have and may continue to have an adverse impact the U.S. regulatory landscape, markets and investor behavior, which could have a negative impact on the Fund’s investments and operations. The change in administration resulting from the 2024 United States national elections could result in significant impacts to international trade relations, tax and immigration policies, and other aspects of the national and international political and financial landscape, which could affect, among other things, inflation and the securities markets generally. Other unexpected political, regulatory and diplomatic events within the U.S. and abroad may affect investor and consumer confidence and may adversely impact financial markets and the broader economy. For example, ongoing armed conflicts between Russia and Ukraine in Europe and among Israel, Iran, Hamas and other militant groups in the Middle East, have caused and could continue to cause significant market disruptions and volatility within the markets in Russia, Europe, the Middle East and the United States. The hostilities and sanctions resulting from those hostilities have and could continue to have a significant impact on certain Fund investments as well as Fund performance and liquidity. The economies of the United States and its trading partners, as well as the financial markets generally, may be adversely impacted by trade disputes and other matters. For example, the United States has imposed trade barriers and restrictions on China. In addition, the Chinese government is engaged in a longstanding dispute with Taiwan, continually threatening an invasion. If the political climate between the United States and China does not improve or continues to deteriorate, if China were to attempt invading Taiwan, or if other geopolitical conflicts develop or worsen, economies, markets and individual securities may be adversely affected, and the value of the Fund’s assets may go down. A public health crisis and the ensuing policies enacted by governments and central banks may cause significant volatility and uncertainty in global financial markets, negatively impacting global growth prospects. As the COVID-19 global pandemic illustrated, such events may affect certain geographic regions, countries, sectors and industries more significantly than others. Advancements in technology may also adversely impact markets and the overall performance of the Fund. For instance, the economy may be significantly impacted by the advanced development and increased regulation of artificial intelligence. Additionally, cyber security breaches of both government and non-government entities could have negative impacts on infrastructure and the ability of such entities, including the Fund, to operate properly. These events, and any other future events, may adversely affect the prices and liquidity of the Fund’s portfolio investments and could result in disruptions in the trading markets.
First Trust Merger Arbitrage ETF | Cyber Security Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock CYBER SECURITY RISK. The Fund is susceptible to operational risks through breaches in cyber security. A breach in cyber security refers to both intentional and unintentional events that may cause the Fund to lose proprietary information, suffer data corruption or lose operational capacity. Such events could cause the Fund to incur regulatory penalties, reputational damage, additional compliance costs associated with corrective measures and/or financial loss. Cyber security breaches may involve unauthorized access to the Fund’s digital information systems through “hacking” or malicious software coding but may also result from outside attacks such as denial-of-service attacks through efforts to make network services unavailable to intended users. In addition, cyber security breaches of the issuers of securities in which the Fund invests or the Fund’s third-party service providers, such as its administrator, transfer agent, custodian, or sub-advisor, as applicable, can also subject the Fund to many of the same risks associated with direct cyber security breaches. Although the Fund has established risk management systems designed to reduce the risks associated with cyber security, there is no guarantee that such efforts will succeed, especially because the Fund does not directly control the cyber security systems of issuers or third-party service providers.
First Trust Merger Arbitrage ETF | Depositary Receipts Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock DEPOSITARY RECEIPTS RISK. Depositary receipts represent equity interests in a foreign company that trade on a local stock exchange. Depositary receipts may be less liquid than the underlying shares in their primary trading market. Any distributions paid to the holders of depositary receipts are usually subject to a fee charged by the depositary. Holders of depositary receipts may have limited voting rights, and investment restrictions in certain countries may adversely impact the value of depositary receipts because such restrictions may limit the ability to convert the equity shares into depositary receipts and vice versa. Such restrictions may cause the equity shares of the underlying issuer to trade at a discount or premium to the market price of the depositary receipts.
First Trust Merger Arbitrage ETF | Equity Securities Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock EQUITY SECURITIES RISK. The value of the Fund’s shares will fluctuate with changes in the value of the equity securities in which it invests. Equity securities prices fluctuate for several reasons, including changes in investors’ perceptions of the financial condition of an issuer or the general condition of the relevant equity market, such as market volatility, or when political or economic events affecting an issuer occur. Common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase. Equity securities may decline significantly in price over short or extended periods of time, and such declines may occur in the equity market as a whole, or they may occur in only a particular country, company, industry or sector of the market.
First Trust Merger Arbitrage ETF | Health Care Companies Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock HEALTH CARE COMPANIES RISK. Health care companies, such as companies providing medical and healthcare goods and services, companies engaged in manufacturing medical equipment, supplies and pharmaceuticals, as well as operating health care facilities and the provision of managed health care, may be affected by government regulations and government health care programs, increases or decreases in the cost of medical products and services and product liability claims, among other factors. Many health care companies are heavily dependent on patent protection, and the expiration of a company’s patent may adversely affect that company’s profitability. Health care companies are also subject to competitive forces that may result in price discounting, may be thinly capitalized and susceptible to product obsolescence.
First Trust Merger Arbitrage ETF | Index Or Model Constituent Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock INDEX OR MODEL CONSTITUENT RISK. The Fund may be a constituent of one or more indices or ETF models. As a result, the Fund may be included in one or more index-tracking exchange-traded funds or mutual funds. Being a component security of such a vehicle could greatly affect the trading activity involving the Fund’s shares, the size of the Fund and the market volatility of the Fund. Inclusion in an index could increase demand for the Fund and removal from an index could result in outsized selling activity in a relatively short period of time. As a result, the Fund’s net asset value could be negatively impacted and the Fund’s market price may be below the Fund’s net asset value during certain periods. In addition, index rebalances may potentially result in increased trading activity in the Fund's shares.
First Trust Merger Arbitrage ETF | Large Capitalization Companies Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock LARGE CAPITALIZATION COMPANIES RISK. Large capitalization companies may grow at a slower rate and be less able to adapt to changing market conditions than smaller capitalization companies. Thus, the return on investment in securities of large capitalization companies may be less than the return on investment in securities of small and/or mid capitalization companies. The performance of large capitalization companies also tends to trail the overall market during different market cycles.
First Trust Merger Arbitrage ETF | Leverage Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock LEVERAGE RISK. Leverage may result in losses that exceed the amount originally invested and may accelerate the rates of losses. Leverage tends to magnify, sometimes significantly, the effect of any increase or decrease in the Fund’s exposure to an asset or class of assets and may cause the value of the Fund’s shares to be volatile and sensitive to market swings.
First Trust Merger Arbitrage ETF | Liquidity Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock LIQUIDITY RISK. The Fund may hold certain investments that may be subject to restrictions on resale, trade over-the-counter or in limited volume, or lack an active trading market. Accordingly, the Fund may not be able to sell or close out of such investments at favorable times or prices (or at all), or at the prices approximating those at which the Fund currently values them. Illiquid securities may trade at a discount from comparable, more liquid investments and may be subject to wide fluctuations in market value.
First Trust Merger Arbitrage ETF | Management Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock MANAGEMENT RISK. The Fund is subject to management risk because it is an actively managed portfolio. In managing the Fund’s investment portfolio, the portfolio managers will apply investment techniques and risk analyses that may not produce the desired result. There can be no guarantee that the Fund will meet its investment objective.
First Trust Merger Arbitrage ETF | Market Maker Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock MARKET MAKER RISK. The Fund faces numerous market trading risks, including the potential lack of an active market for Fund shares due to a limited number of market markers. Decisions by market makers or authorized participants to reduce their role or step away from these activities in times of market stress could inhibit the effectiveness of the arbitrage process in maintaining the relationship between the underlying values of the Fund’s portfolio securities and the Fund’s market price. The Fund may rely on a small number of third-party market makers to provide a market for the purchase and sale of shares. Any trading halt or other problem relating to the trading activity of these market makers could result in a dramatic change in the spread between the Fund’s net asset value and the price at which the Fund’s shares are trading on the Exchange, which could result in a decrease in value of the Fund’s shares. This reduced effectiveness could result in Fund shares trading at a discount to net asset value and also in greater than normal intraday bid-ask spreads for Fund shares.
First Trust Merger Arbitrage ETF | Market Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock MARKET RISK. Market risk is the risk that a particular investment, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by real or perceived adverse economic, political, and regulatory factors or market developments, changes in interest rates and perceived trends in securities prices. Shares of the Fund could decline in value or underperform other investments. In addition, local, regional or global events such as war, acts of terrorism, market manipulation, government defaults, government shutdowns, regulatory actions, political changes, diplomatic developments, the imposition of sanctions and other similar measures, spread of infectious diseases or other public health issues, recessions, natural disasters, or other events could have a significant negative impact on the Fund and its investments. Any of such circumstances could have a materially negative impact on the value of the Fund’s shares, the liquidity of an investment, and may result in increased market volatility. During any such events, the Fund’s shares may trade at increased premiums or discounts to their net asset value, the bid/ask spread on the Fund’s shares may widen and the returns on investment may fluctuate.
First Trust Merger Arbitrage ETF | Merger Arbitrage Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock MERGER ARBITRAGE RISK. Investments in companies that are the subject of a publicly-announced transaction carry the risk the transaction is renegotiated, takes longer to complete than originally planned and that the transaction is never completed. Any such event could cause the Fund to incur a loss. In the case of an investment in a potential target company, if the proposed transaction appears likely not to be consummated, in fact is not consummated, or is delayed, the market price of the security will usually decline sharply, resulting in a loss to the Fund. The risk/reward payout of merger arbitrage strategies typically is asymmetric, with the losses in failed transactions often far exceeding the gains in successful transactions. During periods of market stress, the availability of transactions of the type in which the Fund invests may be significantly limited. In the event that the Sub-Advisor cannot find enough securities that satisfy its investment criteria, the Fund may hold a significant amount of cash or cash equivalents. During periods of market stress or when merger and acquisition activity is low, the availability of transactions of the type in which the Fund invests may be significantly limited. To the extent the Fund has a large cash position, the Fund is less able to satisfy its investment objective. As of October 31, 2024, 28.63% of the Fund’s assets consisted of investable cash and/or cash equivalents. Due to the current market environment, it is expected that the Fund may maintain a large cash position for the foreseeable future.
First Trust Merger Arbitrage ETF | Money Market Short Term Securities Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock MONEY MARKET/SHORT-TERM SECURITIES RISK. To the extent the Fund holds cash or invests in money market or short-term securities, the Fund may be less likely to achieve its investment objective. In addition, it is possible that the Fund’s investments in these instruments could lose money.
First Trust Merger Arbitrage ETF | Risk Nondiversified [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock NON-DIVERSIFICATION RISK. The Fund is classified as “non-diversified” under the 1940 Act. As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended. The Fund may invest a relatively high percentage of its assets in a limited number of issuers. As a result, the Fund may be more susceptible to a single adverse economic or regulatory occurrence affecting one or more of these issuers, experience increased volatility and be highly invested in certain issuers.
First Trust Merger Arbitrage ETF | Non US Securities Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock NON-U.S. SECURITIES RISK. Non-U.S. securities are subject to higher volatility than securities of domestic issuers due to possible adverse political, social or economic developments, restrictions on foreign investment or exchange of securities, capital controls, lack of liquidity, currency exchange rates, excessive taxation, government seizure of assets, the imposition of sanctions by foreign governments, different legal or accounting standards, and less government supervision and regulation of securities exchanges in foreign countries.
First Trust Merger Arbitrage ETF | Operational Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock OPERATIONAL RISK. The Fund is subject to risks arising from various operational factors, including, but not limited to, human error, processing and communication errors, errors of the Fund’s service providers, counterparties or other third-parties, failed or inadequate processes and technology or systems failures. The Fund relies on third-parties for a range of services, including custody. Any delay or failure relating to engaging or maintaining such service providers may affect the Fund’s ability to meet its investment objective. Although the Fund and the Fund's investment advisor seek to reduce these operational risks through controls and procedures, there is no way to completely protect against such risks.
First Trust Merger Arbitrage ETF | Portfolio Turnover Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock PORTFOLIO TURNOVER RISK. High portfolio turnover may result in the Fund paying higher levels of transaction costs and may generate greater tax liabilities for shareholders. Portfolio turnover risk may cause the Fund’s performance to be less than expected.
First Trust Merger Arbitrage ETF | Premium Discount Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock PREMIUM/DISCOUNT RISK. The market price of the Fund’s shares will generally fluctuate in accordance with changes in the Fund’s net asset value as well as the relative supply of and demand for shares on the Exchange. The Fund’s investment advisor cannot predict whether shares will trade below, at or above their net asset value because the shares trade on the Exchange at market prices and not at net asset value. Price differences may be due, in large part, to the fact that supply and demand forces at work in the secondary trading market for shares will be closely related, but not identical, to the same forces influencing the prices of the holdings of the Fund trading individually or in the aggregate at any point in time. However, given that shares can only be purchased and redeemed in Creation Units, and only to and from broker-dealers and large institutional investors that have entered into participation agreements (unlike shares of closed-end funds, which frequently trade at appreciable discounts from, and sometimes at premiums to, their net asset value), the Fund’s investment advisor believes that large discounts or premiums to the net asset value of shares should not be sustained. During stressed market conditions, the market for the Fund’s shares may become less liquid in response to deteriorating liquidity in the market for the Fund’s underlying portfolio holdings, which could in turn lead to differences between the market price of the Fund’s shares and their net asset value and the bid/ask spread on the Fund’s shares may widen.
First Trust Merger Arbitrage ETF | Short Sales Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock SHORT SALES RISK. In connection with a short sale of a security or other instrument, the Fund is subject to the risk that instead of declining, the price of the security or other instrument sold short will rise. If the price of the security or other instrument sold short increases between the date of the short sale and the date on which the Fund replaces the security or other instrument borrowed to make the short sale, the Fund will experience a loss, which is theoretically unlimited since there is a theoretically unlimited potential for the market price of a security or other instrument sold short to increase.
First Trust Merger Arbitrage ETF | Significant Exposure Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock SIGNIFICANT EXPOSURE RISK. To the extent that the Fund invests a significant percentage of its assets in a single asset class or the securities of issuers within the same country, state, region, industry or sector, an adverse economic, business or political development may affect the value of the Fund’s investments more than if the Fund were more broadly diversified. A significant exposure makes the Fund more susceptible to any single occurrence and may subject the Fund to greater market risk than a fund that is more broadly diversified.
First Trust Merger Arbitrage ETF | Smaller Companies Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock SMALLER COMPANIES RISK. Small and/or mid capitalization companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, fewer products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.
First Trust Merger Arbitrage ETF | SPAC Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock SPAC RISK. Unless and until an acquisition is completed, a SPAC generally invests its assets (less a portion retained to cover expenses) in U.S. government securities, money market securities and cash. To the extent a SPAC is invested in cash or similar securities, this may affect the Fund’s ability to meet its investment objective. SPACs have no operating history or ongoing business other than seeking acquisitions. The value of a SPAC’s securities is particularly dependent on the ability of its management to identify and complete a profitable acquisition. There is no guarantee that the SPACs in which the Fund may invest will complete an acquisition or that any acquisitions completed by the SPACs in which the Fund may invest will be profitable. SPACs in which the Fund may invest may pursue acquisitions only within a certain industry or geographic location, which may increase the volatility of their prices. An investment in SPACs, which are typically traded in the over-the-counter market, may also have little or no liquidity and may be subject to restrictions on resale.
First Trust Merger Arbitrage ETF | Trading Issues Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock TRADING ISSUES RISK. Trading in Fund shares on the Exchange may be halted due to market conditions or for reasons that, in the view of the Exchange, make trading in shares inadvisable. In addition, trading in Fund shares on the Exchange is subject to trading halts caused by extraordinary market volatility pursuant to the Exchange’s “circuit breaker” rules. There can be no assurance that the requirements of the Exchange necessary to maintain the listing of the Fund will continue to be met or will remain unchanged. The Fund may have difficulty maintaining its listing on the Exchange in the event the Fund’s assets are small, the Fund does not have enough shareholders, or if the Fund is unable to proceed with creation and/or redemption orders.
First Trust Merger Arbitrage ETF | Warrants And Rights Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock WARRANTS AND RIGHTS RISK. Warrants and rights do not carry with them the right to dividends or voting rights with respect to the securities that they entitle their holder to purchase, and they do not represent any rights in the assets of the issuer. As a result, warrants and rights may be considered more speculative than certain other types of investments. In addition, the value of a warrant or right does not necessarily change with the value of the underlying securities. The Fund could lose the value of a warrant or right if the right to subscribe to additional shares is not exercised prior to the warrant’s or right’s expiration date. The market for warrants and rights may be very limited and there may at times not be a liquid secondary market for warrants and rights.
First Trust Merger Arbitrage ETF | First Trust Merger Arbitrage ETF  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)[ctag:span_t-rule1] rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Management Fees[ctag:span_t-indent1] rr_ManagementFeesOverAssets 1.25%
Distribution and Service (12b-1) Fees[ctag:span_t-indent1] rr_DistributionAndService12b1FeesOverAssets none
Other Expenses[ctag:span_t-indent1] rr_OtherExpensesOverAssets 0.45% [1]
Acquired Fund Fees and Expenses[ctag:span_t-indent1-rule] rr_AcquiredFundFeesAndExpensesOverAssets 0.04%
Total Annual Fund Operating Expenses[ctag:span_t-indent1-rule3] rr_ExpensesOverAssets 1.74%
1 Year rr_ExpenseExampleNoRedemptionYear01 $ 177
3 Years rr_ExpenseExampleNoRedemptionYear03 548
5 Years rr_ExpenseExampleNoRedemptionYear05 944
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,052
2021 rr_AnnualReturn2021 0.56%
2022 rr_AnnualReturn2022 3.46%
2023 rr_AnnualReturn2023 2.56%
Year to Date Return, Label rr_YearToDateReturnLabel <span style="font-family:Arial;font-size:9.00pt;margin-left:0.0pt;">Year-to-Date</span>
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2024
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (0.60%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel <span style="font-family:Arial;font-size:9.00pt;margin-left:0.0pt;">Best Quarter</span>
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2023
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 2.20%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel <span style="font-family:Arial;font-size:9.00pt;margin-left:0.0pt;">Worst Quarter</span>
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2023
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (0.62%)
1 Year rr_AverageAnnualReturnYear01 2.56%
Since Inception rr_AverageAnnualReturnSinceInception 1.07%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 04, 2020
First Trust Merger Arbitrage ETF | After tax on distributions | First Trust Merger Arbitrage ETF  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 1.66%
Since Inception rr_AverageAnnualReturnSinceInception 0.74%
First Trust Merger Arbitrage ETF | After tax on distributions and sale of fund shares | First Trust Merger Arbitrage ETF  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 1.51%
Since Inception rr_AverageAnnualReturnSinceInception 0.68%
First Trust Merger Arbitrage ETF | S&P 500® Index (reflects no deduction for fees, expenses or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 26.29%
Since Inception rr_AverageAnnualReturnSinceInception 11.73%
First Trust Merger Arbitrage ETF | S&P Merger Arbitrage Total Return Index (reflects no deduction for fees, expenses or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 5.52% [2]
Since Inception rr_AverageAnnualReturnSinceInception 2.69% [2]
[1] Other Expenses consist of margin interest expense and dividend expense on investments sold short.
[2] Effective as of August 1, 2024, the S&P Merger Arbitrage Total Return Index replaced the Credit Suisse Merger Arbitrage Liquid Index, which is no longer available for use by the Fund.